A video camera or digital still camera, for example, includes an image pickup lens, image pickup means for converting image light that passes through this image pickup lens into an electrical image signal, and camera signal processing means for processing this image signal, from which an output signal is output to the outside and is recorded in a recording medium.
Here, as the image pickup lens, what is called an optical lens is used. Further, image light from an object which passes through this image pickup lens is separated into light of three primary colors red (R), green (G), and blue (B) by a spectroscopic filter, for example; is focused on an image pickup surface in the image pickup means formed of a CCD, a CMOS sensor, and the like; and is converted into an electrical image signal.
On the other hand, miniaturization is rapidly advanced in a video camera or digital still camera, and also the miniaturization is required for an image pickup lens. Accordingly, in order to miniaturize the image pickup lens, one as before in which multiple lenses are combined and used is often replaced with a small one using a single lens or a few lenses. In addition, in order to achieve miniaturization, a lens in prior art is replaced with a lens having a smaller diameter and is replaced with a lens of inexpensive materials for the purpose of price reduction. However, with such miniaturized image pickup lens, it becomes difficult to sufficiently control picture-quality degradation such as so-called chromatic aberration occurred in a lens.
Specifically, in the optical lens, a refractive index of the lens differs at each wavelength of red (R), green (G), and blue (B) separated by, for example, a spectroscopic filter, so that a phenomenon occurs in which a red (R) image is formed outside a green (G) image and a blue (B) image is formed inside the green (G) image, as shown in, for example, FIG. 5. Therefore, there is a problem in which even in the case where a monochrome image is taken, for example, a color blurring (color shift) appears at an edge of the image.
Thus, in order to control the deterioration of picture quality such as color blurring or resolution degradation due to such chromatic difference of magnification (also called lateral chromatic aberration), conventionally a large number of lenses were combined to perform correction inside the image pickup lens. However, in the above-described miniaturized image pickup lens, it becomes difficult to sufficiently control such deterioration of picture quality only inside the image pickup lens.
To cope with this difficulty, an apparatus disclosed in, for example, Published Japanese Patent Application No. H5-3568 is previously proposed as means for controlling the above-described deterioration of picture quality such as color blurring or resolution degradation due to the chromatic difference of magnification.
Specifically, in the apparatus disclosed, image signals of each color of R, G, B derived from a CCD (image pickup device) are once converted into digital data and temporarily stored in individual field memory, respectively; further, based on a driving state of the image pickup lens such as a zoom focal length and a focal position, each image stored in each field memory is enlarged or reduced by individually moving vectors of each entire field memory and then R, G, B are again combined for correcting the color shift occurring in the image pickup lens of a video camera.
Meanwhile, when an image is taken by a small-sized video camera or digital still camera, for example, held by hand, there is a possibility that an image blurring due to so-called camera shake or the like may happen. Thus, for the purpose of removing the disadvantage such as the image blurring, what is called a camera shake correction device is installed in the small-sized video camera or digital still camera. FIG. 6 shows a block diagram of the video camera or digital still camera in which the camera shake correction device is installed.
In FIG. 6, image light from an object (not shown) passing through an image pickup lens 50 forms an image on the image pickup surface of an image pickup means 51 including CCD, CMOS sensors and the like and is converted into an electric image signal including, for example, an intensity (Y) signal and two color-difference (Cb, Cr) signals. The image signal is supplied to a camera-signal processing circuit 52, where signal processing such as so-called γ correction is made to generate an ordinary image signal used for general-purpose video equipment.
On the other hand, in order to detect so-called camera shake, angular velocities due to the camera shake in Pitch and Yaw directions are detected using, for example, two gyro-sensors 53P and 53Y in this example. Further, a zoom focal length of the image pickup lens 50 operated by, for example, a user is detected from the image pickup lens 50. Additionally, to detect the zoom focal length, an operational signal from a manual input means 54 operated by a user for example, can be employed.
Further, the angular-velocity signals detected by the gyro-sensors 53P and 53Y are supplied to high-pass filters (HPF) 55P and 55Y, where DC components are removed; on the other hand, data on the above-described zoom focal length is supplied to a table 56 and necessary operational coefficients are found from those data; and the operational coefficients are supplied to multipliers 57P and 57Y, and are multiplied there by signals from the high-pass filters 55P and 55Y. Furthermore, output signals from the multipliers 57P and 57Y are further supplied to integrators 58P and 58Y, respectively.
Accordingly, information on angles of the image pickup lens 50 varied by the camera shake is derived from those integrators 58P and 58Y. The angular information on the camera shake is supplied to, for example, the image pickup means 51 through limiter circuits 59P and 59Y and a position at which the image signal is taken out from the image pickup means 51 is controlled. Specifically, for example, the image pickup means 51 is provided with a image pickup surface wider than a size of the original image, and a necessary image is taken out from the image pickup surface so as to cancel out the fluctuation due to camera shake.
In this way, so-called camera shake correction is performed in the small-sized video camera or digital still camera. Additionally, the following methods are also practiced as means for performing the camera shake correction other than controlling the position to take out the image signal from the camera means 51 as described above, in which all image signals picked up by the image pickup means 51 are once stored in a memory 60 and then a position at which the image signal is read out from the memory 60 is controlled, or a partial lens position of the image pickup lens 50 is shifted for the correction.
Furthermore, the information on angles of the image pickup lens 50 varied by the camera shake can also be taken out by other means than that using the above-described gyro-sensors 53P and 53Y; for example, as shown in FIG. 7, by storing the image signal from the image pickup means 51 in a frame memory 61 and then comparing the image signals prior to and subsequent to the frame memory 61 with each other in a comparator circuit 62, the angular information on the camera shake can be calculated from displacement of an image in the background and the like. In addition, the calculated angular information on camera shake can be utilized in all the above-described camera shake correction means.
However, it is verified that, when such camera shake correction is performed, if the compensation for the picture-quality deterioration such as color blurring or resolution degradation due to the chromatic difference of magnification is attempted, sufficient correction cannot be made. Specifically, in the above-described device, when the vector of each entire field memory is moved, the center must correspond with an optical axis of the image pickup lens; however, if the camera shake correction is performed, the position of the optical axis is moved and it is difficult to correspond with the center.
For this reason, the compensation for picture-quality deterioration due to chromatic aberration, for example, could not be performed simultaneously with the camera shake correction in the past. However, in conventional kinds of system having a small number of pixels, the picture-quality deterioration, for example, due to chromatic aberration is less noticeable, particularly when taking a picture which requires the camera shake correction. Lately, however, as the result that the increase in the number of pixels of a picture has been demanded, the influence of the picture-quality deterioration due to chromatic aberration or the like becomes conspicuous under every situation.
Specifically, when compensation for the picture-quality degradation is performed by making the image of each color enlarged and reduced as described above, there has been such a problem that the camera shake correction can not be performed concurrently. Therefore, inventors of this patent application have previously proposed an image recording and reproducing apparatus, an image pickup apparatus, and a chromatic aberration correcting method to solve the above described problem between the compensation for the picture-quality degradation and the camera shake correction in Japanese Patent Application No. 2002-59191.
However, as a result of verification of the color shift occurred in the image pickup lens in the above-described small-sized video camera or digital still camera, an amount of color shift occurring is also influenced by an aperture amount of an iris and a lens image height of an object in the image pickup lens. It should be noted that the lens image height of the object is a distance from optical axis-centered coordinates in an image of the relevant object.
FIG. 8 shows a relation between an aperture amount of an iris (horizontal axis) and a shift amount in a picture-forming position of light of three primary colors (red: R, green: G, and blue: B) (vertical axis) at points of the image height 0.0, the image height 0.5, the image height 0.7, the image height 0.9, and the image height 1.0 respectively from the bottom, where the lens center is expressed as the image height 0.0 and a lens edge is expressed as the image height 1.0. On the left side of the diagram is shown the characteristic of a vertical plane (TANGENTIAL) to the optical axis and on the right side of the diagram is shown the characteristic of a horizontal plane (SAGITIAL) to the optical axis. Further, a zoom position and a focal position are fixed at certain points.
Specifically, in each of the curves shown in FIG. 8 is plotted for each color (R, G, B) an amount of aberration generated depending on the position where light of the point of each image height passes in the iris aperture shown in FIG. 5. Note that in the TANGENTIAL characteristic curves on the left side, the positive side of the horizontal axis shows the characteristic of light passing through an upper part of the iris aperture and the negative side thereof shows the characteristic of light passing through a lower part of the iris aperture. Further, the negative side is omitted in the SAGITIAL characteristic curves on the right side, because the characteristic appears symmetrically.
Furthermore, a unit of the vertical axis is a millimeter for both TANGENTIAL and SAGITIAL, and the positive side shows the outer side of the lens and the negative side shows the side close to the center of the lens. Moreover, the characteristic curve of green (G) passes through the zero point, and the other characteristic curves of red (R) and blue (B) are shown by relative values to green (G).
Accordingly, it is understood from FIG. 8 that the direction where the chromatic aberration appears and the amount thereof are fluctuated depending on the aperture amount of the iris in the image pickup lens and the lens image height of the object. Hence, there arises necessity for correcting not only the chromatic aberration occurred in the above-described lens, but also color shift generated in the image pickup lens with respect to the aperture amount of the iris and the lens image height of the object.
This application is made in view of the above and aims to solve the problems of: picture-quality degradation such as the color blurring and resolution degradation caused by the magnification chromatic aberration due to the miniaturization of the image pickup lens and the like, difficulties in sufficiently controlling such picture-quality degradation only by the image pickup lens, and further the necessity for correcting the color shift generated in the image pickup lens also with respect to the aperture amount of the iris in the image pickup lens and the lens image height of the object.